Material recycling has become an important industry in recent years due to decreasing landfill capacity, environmental concerns and dwindling natural resources. Many industries and communities have adopted voluntary and mandatory recycling programs for reusable materials. Solid waste and trash that is collected from homes, apartments and companies often combine several recyclable materials into one container. When brought to a processing center, the recyclable materials are frequently mixed together in a heterogenous mass of material. Mixed recyclable materials include newspaper, clean mixed paper, magazines, aluminum cans, plastic bottles, glass bottles and other materials that may be recycled.
Disc apparatus or “disc screens” are increasingly used to separate streams of mixed recyclable materials into respective streams or collections of similar materials. This process is referred to as “classifying”, and the results are called “classification”. A disc screen typically includes a frame in which a plurality of rotatable shafts are mounted in parallel relationship. A plurality of discs are mounted on each shaft and a chain drive commonly rotates the shafts in the same direction. The discs on one shaft interleave with the discs on each adjacent shaft to form screen openings between the peripheral edges of the discs. The size of the openings determines the dimension (and thus the type) of material that will fall through the screen. Rotation of the discs, which have an irregular outer contour, agitates the mixed recyclable materials to enhance classification. The rotating discs propel the larger articles which are too big to fall between the discs across the screen. The general flow direction extends from an input area where the stream of material pours onto the disc screen to an output where the larger articles pour off of the disc screen. The smaller articles fall between the discs onto another disc screen or a conveyor, or into a collection bin.
There is a substantial market for recycled newspaper and/or clean mixed paper. Therefore, it is important that any disc screen which is designed to classify mixed recyclable materials be capable of thoroughly separating newspaper and/or clean mixed paper from the heterogenous mass of material. Prior disc screen apparatus designed to handle a stream of mixed recyclable materials have included multiple disc screens with different fixed angles of inclination and different sizes of openings between the discs. They are capable of separating broken glass from containers. They are also capable of separating clean mixed paper and newspaper from the stream of mixed recyclable materials. CP Manufacturing, Inc. of National City, Calif., the assignee of the subject application, sells the NEWScreen™ recyclable waste classifier with multiple overlapping screens that can be simultaneously tilted at various angles to improve the efficiency of separation of mixed recyclable materials. See U.S. Pat. No. 6,250,478 granted Jun. 26, 2001 to Robert M. Davis and entitled “Stepped Disc Screens of Unequal Inclination Angles for Conveying and Grading Recycling Materials.” However, a consistent problem that has been encountered with apparatus for classifying mixed recyclable materials using multiple disc screens is the fact that all of the disc screens must be tilted together. This may improve the separation on one of the screens while impairing the separation on the other screen(s).
In order to overcome these drawbacks, recycling apparatuses have been constructed with a pair of disc screens, one feeding the next, with the angle of each screen being independently adjustable. The output end of the first screen is spaced a considerable distance above the input end of the second screen. Where such apparatuses are used to classify mixed recyclable materials there are inefficiences that result from the waste having to spill off the upper end of one screen onto the lower end of the next screen. Also, the disc spacings and contours may vary between the screens further reducing the efficiency of the overall classification. If the first screen is too steeply angled, newspaper will fall off its rearward end along with containers and this is undesirable. If the first screen is not inclined enough, then the containers will not fall off its rearward end and this is also undesirable. Furthermore, the use of two tiered or overlapping screens necessarily increases the overall size, cost and complexity of this type of waste sorting apparatus.